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You have too much air or too little fuel getting into the engine. Look for easy things first. Vacuum leaks in hoses particularly at rear of engine. It helps to take off the plastic cover so you can inspect the many hoses. The hose to the brake booster is particularly prone to deterioration. Check PCV valve is snug on passenger side valve cover. Look online at methods for vac leak detection on a running engine. check for splits in air duct after the MAF sensor. if the fuel filter hasn’t ever been changed, maybe change that.So I just got the same codes on my 2004 Eddie Bauer 5.4 4wd that has 225,000 on it. We got the p0128 code and the p0171 code a few weeks ago and my husband changed out the thermostat and the check engine light didn't go out so I had it cleared. It came back on today and I had it scanned again and it gave the p0171 and p0174 codes today. It is running just fine, just has the check engine light on. I read through the stuff above and I am wondering what are the simplest things to start with to try. My husband is going to be unavailable to work on it for the next two weeks so I have to drive it every day. Any ideas?